I'd imagine they'd boot up a game without having played the tutorial, spend 30 seconds trying to figure out how to place a brick, and then totally give up once they find out it's not as easy as pointing and clicking like an ape and start screaming into the mic about how boring the game is
Like that one other YouTuber who's first online experience managed to land on the community's most unfun pretentious hard-ass Medieval RP and then ended up in a weird rape RP with one of the admins. This is the best way the experience could possibly have gone because it was the only server with players. A youtuber playing the game would probably just turn Blockland into an even bigger laughing stock for Roblox and inattentive children with no net positive impact on the game. I'd wager the best course of action at this point is up-selling the stuff out of the game and try to fool people into thinking that there's tons of fun servers to play like the steam trailer does.
Or hosting more good servers I guess. There was someone a while back who recommended we all boot up servers during the sale so that people who bought it on sale would have more incentive to stick around. I bet a youtube video would work in that scenario.